The purpose of this proposal is to examine whether during heavy metal toxication mistakes are made in the synthesis of cytochromes so that the porphyrin does not contain iron. Animals will be exposed to high concentrations of metals either through diets or through the atmosphere. Because prophyrins containing closed shell metals, unlike iron prophyrins, are fluorescent, incorporation of metals such as lead or zinc can be detected in low levels by examining the luminescence of tissue such as lung or liver, or tissue fragments such as mitochondria or endoplasmic reticulum. The incorporation of metals into cytochromes will be considered as a possibility of a cause of metal toxicosis and may provide a means to diagnose metal intoxication caused by environmental pollution. Finally, the role of the enzyme, ferrochelatase, in inserting the metal into the porphyrin will be examined in vitro and the results compared with the in vivo findings.